This invention pertains generally to filters for use in waste water treatment, particularly to filters intended for filtering liquid effluent exiting a septic tank prior to final introduction of the liquid to a distribution field. The invention has utility in both gravity fed septic to field distribution systems as well as in pumped outlets such as those used in low pressure mound sanitary drainage systems.
Conventional drainage fields for receiving the output of septic tank sewage effluent are generally in the form of network of perforated finger pipes connected to an outlet of the septic tank and situated in trenches on top of a filter bed generally consisting of rock, crushed stone, gravel, sand, or a combination thereof. Such systems normally operate by gravity flow, however, it is common practice to connect a pump to the septic tank to aid in moving the sewage effluent from the septic tank and through the drainage field, particularly where required by the lay of the land or other criteria leading to the adoption of such a design. The sewage effluent is distributed through the network of perforated pipes and trickles onto and through the filter bed, where its nutrient content is reduced by microbial action. After passing through the filtering material, the sewage effluent is absorbed by the soil surrounding and underlying the trench. Critical to the continued operation of such a system is the maintenance of an open system of perforations in the pipes connected to the outlet of the septic tank as well as in the filter bed and underlying soil. Usefulness is limited, however, by clogging of the openings in the drain field finger pipes, stone, sand, and soil pores from semisolid debris flowing from the septic tank or by solids such as leaves and grass which can enter the effluent tank during servicing or resulting from a loosely fitting effluent tank cover. As the pipe openings, filter bed, and underlying soil become blocked, flow of effluent is reduced and the sanitary drainage system can be rendered inoperative.
In order to prevent the drain field finger pipe openings, filter bed, and underlying soil from clogging, solid material present in the effluent should be removed prior flow into the drain field. Currently available effluent apparatus include filtering devices having a filter disposed in fluid connection between the septic tank and the drain field, such as those described in U.S. Pat. Nos. 3,332,552; 4,710,295; 5,382,357; 5,580,453; 5,593,584; 5,683,577; 5,762,790; 5,762,793; 6,136,190; and 6,267,882. Other filters have been employed at the input of an effluent pump, for instance those devices and systems described in U.S. Pat. Nos. 5,492,635; 5,427,679; and 4,439,323, and filters in fluid connection to the input of a septic pump, as described, for instance, in U.S. Pat. No. 5,582,716. Solid material present in effluent should be removed prior to the flow into the drain field and can be filtered by such devices, thereby helping to prevent clogging. However, the filtering orifices defined by these devices do not filter efficiently and effectively, and frequently become clogged, requiring cleaning and servicing of the filtering apparatus.
Common to many of the filters disclosed in the prior art is a canister wall or housing in which the filter is located. When the filter becomes clogged and requires cleaning or replacement, many filters lose some or most of the debris that has been held back. Frequently, the entire canister needs to be removed from the fluid piping or chamber system in which it is installed. Frequently, the outlet tees containing the canisters are not aligned with an access port to the septic tank in which it is located, thus requiring some manipulation of the clogged canister during removal or replacement, making most current filters unusable because of their rigidity. Any manipulation tends to disturb some of the material extracted by the filter, making the whole process somewhat disagreeable, and contributing to the outflow of particulate matter into the finger field, which is just what the filter is intended to prevent. Even more disagreeable are those filters in the prior art that, due to the high initial cost, are often disassembled, cleaned and reinstalled rather than being simply withdrawn and replaced with a new filtering unit.
What is needed is a low cost filtering element. What is also needed is a filtering element that is light weight and flexible even in cold climates so that it is easily replaced even in less than optimum physical arrangements. What is further needed is a filtering element that is sufficiently adaptable to fit a variety of sizes of filtering chambers, tees and baffles. What is additionally needed is a replacement kit that provides a means for preventing outflow of particulates into the finger field during the filter replacement process. What is also needed is a filter having a large total filtering surface area so that efficient and effective filtering action occurs at good flow rates. What is further needed is a filter that can remove the smallest particulates of hair, tissue, lint, and other materials yet is easily replaced and properly discarded at the end of its useful life.
A filter element of the present invention is intended for use in waste water discharge systems. The filter element generally comprises an axial support of a pre-selected length. A handle is fixed to the axial support to facilitate the placement and withdrawal of the filter element. A plurality of bristles are fixed to and extend radially outward from the axial support to an outer margin. The outer margin of the bristles defines a substantially continuous surface generally symmetric about the axial support. The outer margin generally includes a plurality of portions defining a first selected radius of the filter element. At least two of the plurality of portions are separated by an intermediate portion wherein the bristles terminate short of the first selected radius.
The axial support desirably occupies as little of the cross-section of the filter as possible. The axial support is preferably somewhat flexible to ease the installation and withdrawal of the filter element. The can be achieved by having the axial support comprise a spiral wound set of wires, the bristles being captured between the set of wires. The wires can be of any suitable material such as galvanized steel, aluminum, or stainless steel, the stainless steel being preferred due to the longevity imparted to the filter by such a construction.
The bristles can be straight, crimped, convoluted or otherwise shaped to maximize the filtering efficiency of the filter without presenting undue back pressure to the passing fluid. While the bristles can have a cross-section that is round or oval, they preferably have a cross-section that enhances the surface area of the bristle fibers such as hexagonal, pentagonal, square, triangular, or even star shaped to enhance the small particle filtering capacity. The bristles should be somewhat flexible to aid in the installation and withdrawal of the filtering element. The bristles should also be resilient or shape retentive so that upon placement of the filter element into a chamber, the filtering element will generally self align in the middle of the chamber and will not be significantly deformed by the flow of fluid through the filter, even when partially loaded with extracted particulate material from the waste water. The bristles are desirably resistant to biological degradation and generally inert to the typical chemicals present in waste water. Suitable materials for forming the bristles include synthetic polymeric materials such as aliphatic polyamides, aromatic polyamides, polyolefins, polyvinyl chloride, polyurethane, fluoropolymers, polyvinylidene chloride, polystyrene and styrene copolymers, and particularly polyesters, polypropylene, polyethylene or nylon. The outer margin of the bristles is generally axially symmetric with respect to the axial support, but is not of uniform diameter throughout the length of the filtering element. The outer margin can include several convolutions or indentations, which typically enhance the filtering function of the filter element by causing selective settling of the particulate matter filtered from the waste water in preferred spaced locations along the length of the filter rather than uniformly, or with a constant gradient, throughout the length of the filter. Preferably there is an additional indentation aligned with the expected location of any outlet to the finger field. The outermost dimension of the bristles forming the outer margin is preferably slightly larger than the expected interior dimension of the chamber or pipe into which the filter is expected to be installed to ensure that no significant portion of the waste water passes around the filter. A wide range of filtering capacities can be created by using bristles of different cross-section, shape, diameter, polymeric make-up and density.
The handle must be securely fixed to the axial support so that even after prolonged presence in a septic tank, the handle will afford easy handling of the filtering element. A preferred form for the handle is simply a unitary extension of the axial support. Preferably the handle extends radially to only one side of the axial support by a distance sufficient to have a terminal portion extend beyond the outermost portion of the outer margin defined by the bristles. Further, the handle preferably includes a further portion that extends parallel to the axial support at a position separated from the axial support by a distance greater than the outer margin defined by the bristles. This later feature allows the handle to overlie a terminal end of any pipe or chamber into which the filter element can be inserted, thereby ensuring that the filtering element is secured in place within the filtering chamber, and does not slip out the bottom of the filtering chamber.
The replacement of a filtering element of the present invention is facilitated by the use of a shield member for temporarily covering the outlet to the finger field during the replacement. The shield member generally comprises a sheet of material that is generally conformable to the inside surface of the filter receptacle. The shield member has a length dimension sufficient to cover the outlet leading to the finger field to block any outward flow of waste water during replacement of the filter element. The shield member preferably has a width dimension selected so that the margins defining the width dimension are spaced from each other by a distance sufficient to allow the shield member to pass by the handle when inserted into the filter receptacle. The deformable character of the bristles of the filter element of the present invention facilitate the installation of the shield at the time of filter replacement. With the shield member in place, the existing filter can be quickly withdrawn from the filter receptacle and a new filter slipped in to replace the old filter. With the new filter in place so that the handle is aligned with the space between the lateral margins of the shield member, the shield member can be slipped out of the filter receptacle, thus re-opening the outlet to the finger field and reinitiating the filter process.
The filtering elements of the present invention can be used singly or can be grouped in a parallel array to process a larger volume of liquid or a highly contaminated flow of liquid as might be present in a commercial situation. The filtering element have particular utility in septic systems, but can be used in other circumstances where a low to moderate rate of flow axially through a generally tubular opening is expected.
With these general characteristics in mind, a further understanding of certain features and advantages will emerge from a study of the following description and the accompanying figures of a preferred embodiment illustrating the best mode of carrying out the invention.